11/128" is how KMC refer to their 10s etc chains. It is an accurate indication of the internal width of the chain. In practice you need lateral clearance from the sides of the teeth to the chain. The amount of clearance you need varies depending on
- 1x,2x or 3x
- singlespeed or derailleur
- if muddy conditions are likely
- if burring of the teeth is likely.
A few years ago I built a bike up using an old set of triple chainrings and a 9s chain. I nearly drove myself berserk trying to get the chain to downshift off the middle chainring. I eventually concluded that the chain was just too snug on the teeth of the chainring; a different chain transformed it out of all recognition. 1/128" clearance evidently made a difference!
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